(multiple brand) POST-Code display (2 Digit 7-Segment Display)
Logs
dateType
Sensing / Monitoring
actActions
See all boards with this chip See all cards with this chip
doc No chip documents available
drv No drivers available
notes Notes

The POST-Code Display (or Port 80h Display) is a diagnostic tool consisting of a two-digit, 7-segment LED module. It provides real-time visual feedback during the Power-On Self-Test (POST) sequence, allowing for hardware troubleshooting before video output is initialized.

Technical Function

  • Port Monitoring: In standard x86 architecture, the BIOS/UEFI outputs status codes to an I/O port. While Port 80h is the industry standard for AT/ATX clones, legacy and proprietary systems utilize a variety of alternative addresses:

    • Port 80h: Standard AT/ATX and most clones.
    • Port 84h: Standard for Compaq systems.
    • Port 90h / 190h: Used by IBM PS/2 Models 25 & 30.
    • Port 680h / 3BCh: Used by IBM PS/2 Models 50 and up (Microchannel architecture).
    • Port 300h: Commonly found on EISA systems and some Award BIOS implementations.
    • Port 378h: Utilized by Olivetti (mapping through the LPT/Parallel port).
    • Port 60h: Used by original PC/XT architecture (often monitoring the 8255 PPI).

  • Hexadecimal Feedback: The display latches a 1-byte value (00-FF) from the bus (ISA, MCA, PCI, or LPC). Each code represents a specific initialization step.

  • Diagnostics: If a system hangs, the code identifies the failed process (e.g., RAM detection, VGA init).

Implementation

Originally limited to dedicated expansion cards, integrated onboard displays became a signature feature of high-end enthusiast motherboards in the late 1990s and 2000s.

  • Notable Brands: Popularized by Abit (Port 80), EPoX, ASUS (Q-Code), and EVGA.
  • Driving Logic: While the display is a standard LED component, the driving logic is typically handled by a Super I/O chip, CPLD, or FPGA that "snoops" the relevant bus for specific I/O writes.

Some common codes to help troubleshoot issues:

  • (any) -- or 00: no CPU activity
  • (Award) C1 - C6: RAM problems
  • (Award) 0D: VGA initialization
  • (Award) 31: reached POST screen
  • (AMI) D1 - D5: RAM problems
  • (AMI) 2A: VGA initialization

Refer to the following blog articles for more detailed info on:

Last updated 2026-01-16T12:32:59Z
image1 Image 1 of 2 (Markus Kuhn)
image2 Image 2 of 2 (Helen_Croft)

Disclaimer

The info found in this page might not be entirely correct. Check out this guide to learn how you can improve it.